The present invention relates to polydicyclopentadiene (polyDCPD) materials and methods for synthesizing these materials. More particularly, the present invention relates to the use of Ring Opening Metathesis Polymerization (ROMP) reactions for synthesizing polyDCPD.
PolyDCPD is an extremely technologically and commercially important polymer material. It is a tough, rigid, thermoset polymer with high modulus, excellent impact strength, and excellent chemical resistance. As a result of these combination of properties, the material finds extensive use in a variety of applications that require toughness and chemical resistance including use in industrial housings, chlorine cell covers, waste water treatment equipment, water vehicles, and snow mobiles.
Because of the commercial importance of polyDCPD, there has been extensive research into methods for producing this material. One method that has attracted considerable attention is the production of polyDCPD by the ROMP of dicyclopentadiene (DCPD) monomers using a metathesis catalyst system. The polyDCPD produced via the ROMP reaction may be post cured to increase the cross-link density of the polyDCPD material. The original catalyst systems used for the ROMP of DCPD were of the Ziegler type. These catalysts were rather ill-defined, and were formed by the reaction of an early transition metal halide with a reducing agent such as an alkyl aluminum halide. A variety of other catalyst systems have also been developed based on tungsten or molybdenum; however, all of the previous catalyst systems have at least two important drawbacks.
First, the previous catalyst systems are all easily poisoned by impurities and the monomer starting material must therefore be highly purified and water and alcohols must be excluded from the reaction mixture. See for example U.S. Pat. No. 4,661,575 which states that "the presence of water interferes with polymerization of both the catalyst and the activator" and "the water content of the starting material should be below about 100 p.p.m." The monomer starting material used in the conventional processes usually consists of greater than about 99% pure DCPD monomer and this starting material is considerably more expensive than less pure, low grade, monomer. In fact, in the conventional processes the low grade, commercially available monomer must be preprocessed before it may be used as the starting material in the ROMP reaction. U.S. Pat. No. 4,661,575 states that "the preferred commercially available material [endo-DCPD] normally has a purity of 96-97%," and "the commercially available material should be purified to prevent impurities from inhibiting the polymerization." In addition to the added expense of purchasing and purifying the starting material for use in the conventional processes, a further drawback of having to use highly pure monomer is that the starting material must be stored under stringent conditions to ensure that it is not contaminated. These drawbacks result in increased cost and increased difficulty in handling of the raw materials; considerations which become extremely important in the large-scale production of polyDCPD articles.
The second drawback of the conventional processes is that not only are the starting materials expensive and difficult to handle but the polyDCPD produced using these processes may possess undesirable physical characteristics. Most importantly, some of the polyDCPD formulations produced using the conventional catalyst systems are blackened or darkened in appearance and are opaque. The black color of these materials increases the difficulty of producing different colored polyDCPD articles by the addition of pigments or dyes to the polymer material. Additionally, since the materials are opaque they cannot be used in applications that require transparent or translucent materials. These undesirable physical characteristics reduce the possible uses of the conventionally produced materials in some industrially and commercially important applications.
For these reasons there exists a need for a method for producing polyDCPD that does not require the use of highly pure DCPD monomer as a starting material. It would further be desirable to produce a polyDCPD material that is transparent or translucent in the absence of additives and that can be produced in a variety of colors by the addition of dyes or pigments while still retaining excellent physical and chemical properties.